Ebola's Hidden Target: Virus Transmission to and Accumulation within Skin

Ebola virus (EBOV), the causative agent of Ebola virus disease (EVD), remains one of WHOs top ten threats to global health. Infectious EBOV virions can be found on the surface of skin late during systemic infection and passed from the deceased through skin-to-skin contact. Here, we assess viral load and antigen expression in the skin of EBOV-infected non-human primates (NHP) and mouse adapted-EBOV (ma-EBOV) - infected mice and use the low containment viral model, rVSV/EBOV GP, to mechanistically define skin infection in mice. Viral RNA peaked within the skin proximal to the site of injection in EBOV-infected NHPs on day 6. In contrast, mouse skin sites distal to the site of ma-EBOV injection achieved maximal viral loads by day 3. At late times of infection, viral antigen-positive cells co-localized with markers for endothelial, stromal, and immune cells in the dermis. Epidermal cells within and surrounding hair follicles also harbored viral antigen, suggesting a potential mechanism of virus trafficking to the epidermal surface. Despite robust viral infection, distal skin sites of ma-EBOV-infected mice had low expression of proinflammatory stimulated genes. A similar cellular tropism was observed in the skin of mice infected with rVSV/EBOV GP, with discrete focal areas of intense infection. When virus was applied to the surface of gently abraded skin to remove the stratum corneum, epidermal keratinocytes were robustly infected, followed by systemic viral dissemination. To define cell surface receptors critical for virus trafficking to and replication within the skin, mice lacking the phosphatidylserine receptors were infected intraperitoneally with rVSV/EBOV GP. At day 3 of infection, skin distal to the site of infection of TIM-1 knock out (KO) mice had significantly lower levels of infectious virus than the control mice, suggesting that TIM-1 is essential for efficient distribution of virus to the skin. Our findings reveal that EBOV targets specific skin cell populations at late times of viral infection and that the host receptor TIM-1 is required for optimal viral dissemination.